The most varied methods are used for obtaining crude oil. In the development of oil fields, only a part of the available oil may be obtained by spontaneous extraction. After a spontaneous extraction, however, a significant part of the oil remains in the rock. This is what is termed primary extraction, in which the oil comes out of the ground spontaneously without further influence, and therefore leads only to a partial exploitation of the oil reserves. However, the yield can be increased by separating the oil in the rock by displacement processes, as is performed, for example, in the context of what is termed secondary extraction. However, in this case, considerable amounts of oil reserves still remain in capillary rock channels, which oil reserves cannot be separated by a simple pumping or displacement process. Therefore, in the context of what is termed tertiary extraction for example, a liquid having defined rheological behavior is introduced into the rock strata and the capillary channels thereof, in order to displace the crude oil from the capillaries also. For the production of such liquids, polymers of natural origin are also used. Suitable thickening polymers for a tertiary oil extraction must meet a number of specific requirements. In addition to a sufficient viscosity, the polymers must also be very stable thermally, and the thickening effect thereof must also be retained at high salt concentrations. An important class of polymers of natural origin for polymer flooding for obtaining oil comprises polysaccharides, in particular branched homopolysaccharides, that are obtained from glucose, for example beta-glucans. The aqueous solutions of such beta-glucans have advantageous physicochemical properties, in such a manner that they are particularly suitable for polymer flooding of oil-comprising rock strata. Therefore, beta-glucans are suitable as thickeners in the field of tertiary oil extraction.
Beta-glucans are components of cell walls in several microorganisms, in particular in fungi and yeast (Novak, Endocrine, Metabol & Immune Disorders—Drug Targets (2009), 9: 67-75). From the biochemical aspect, beta-glucans are non-cellulosic polymers of beta-glucose linked by beta(1-3)-glycosidic bonds that have a defined branching pattern with beta-(1-6)-linked glucose molecules (Novak, loc. cit.). A multiplicity of closely related beta-glucans has a similar branching pattern such as, e.g., schizophyllan, scleroglucan, pendulan, cinerian, laminarin, lentinan and pleuran, which all have a linear main chain of beta-D-(1-3)-glucopyranosyl units with a single beta-D-glucopyranosyl unit which is (1-6)-linked to a beta-D-glucopyranosyl unit of the linear main chain, with a mean degree of branching of approximately 0.3 (Novak, loc. cit.; EP-B1 463540; Stahmann, Appl Environ Microbiol (1992), 58: 3347-3354; Kim, Biotechnol Letters (2006), 28: 439-446; Nikita, Food Technol Biotechnol (2007), 45: 230-237). At least two of said beta-glucans—schizophyllan and scleroglucan—even have an identical structure and differ only slightly in molecular mass thereof, i.e. in their chain length (Survase, Food Technol Biotechnol (2007), 107-118).
For the use in displacement liquids, beta-glucan-comprising liquids must be made available at the oil production sites. This poses a transport problem to the operators of the production sites, since considerable amounts of beta-glucan-comprising liquids are required in order to obtain a meaningful tertiary yield. Therefore, operators are increasingly changing over to concentrating the beta-glucan-comprising or polysaccharide-comprising liquids, and so the transport expense is smaller. However, this requires a preparation of the concentrated liquids on site, in which the water fractions removed previously are fed back to the concentrated liquid.
Many processes for producing beta-glucans comprise culturing and fermenting microorganisms that are able to synthesize such biopolymers. For example, EP 271 907 A2, EP 504 673 A1 and DE 40 12 238 A1 describe a method in which the fungus Schizophyllum commune is fermented by agitation and with air supply in sections.
The culture medium substantially comprises glucose, yeast extract, potassium dihydrogen-phosphate, magnesium sulfate and water. EP 271 907 A2 describes a method for separating the polysaccharide in which the culture suspension is first centrifuged and the polysaccharide is precipitated from the supernatant with isopropanol. A second method comprises a pressure filtration followed by an ultrafiltration of the resultant solution, without the details of this method having been disclosed. “Udo Rau, “Biosynthese, Produktion und Eigenschaften von extrazellulären Pilz-Glucanen” [Biosynthesis, production and properties of extracellular fungal glucans], post doctoral thesis, Technical University of Brunswick, 1997, pages 70 to 95” and “Udo Rau, Biopolymers, Editor A. Steinbüchel, Volume 6, pages 63 to 79, WILEY-VCH Publishers, New York, 2002” describe the preparation of schizophyllan by continuous fermentation or fermentation in batch mode. “GIT Fachzeitung Labor 12/92, pages 1233-1238” discloses a continuous method for preparing scleroglucans using Sclerotium rolfsii. 
For economic reasons, the concentration of the aqueous beta-glucan solution should be as high as possible to keep the costs of transporting the aqueous glucan solutions from the production site to the use site as low as possible, in particular if the preparation is to be performed within short periods of time.
A system is known, for example, from the prior art EP 2 197 974 A1 for improving oil extraction, using water-soluble polymers.
In addition, WO 2008/071808 A1 discloses a device for producing a water-soluble polymer for tertiary oil recovery.
The document WO 2012/110539 A1 discloses a two-stage method for crude oil extraction wherein an aqueous formulation comprising at least one glucan is injected into a crude oil reservoir through an injection borehole, and crude oil is removed from said reservoir through a production borehole. The aqueous formulation is produced in two stages, an aqueous concentrate of the glucan being produced first and the concentration then being diluted with water on-site to obtain the concentration for use.
From the patent application US 2014/364344 A1 a system and a method are known to produce an aqueous solution from a powder starting material, the solution being usable in tertiary oil recovery. The system comprises a mixer and a plurality of compartments in a tank. The solution can flow through the compartments or can be deviated around one or more compartments. The aqueous solution is adjusted via its residence time inside the respective compartments of the system.
Furthermore, EP 2 344 273 A1 discloses a method using high shear for producing micronized waxes.
The object of the present invention is to provide a method for redispersing polysaccharides, in particular beta-glucans, that are in concentrated form, in order to obtain an aqueous solution comprising polysaccharides, in particular beta-glucans that is suitable for the use in tertiary oil recovery, as is illustrated by a low FR value, in particular by an FR value≤3.0 determined using a membrane that has a pore size of 1.2 μm.